This drug abuse treatment research project will define the full range of program and community based service involvements of 420 outpatient methadone and drug-free clients. All clients will be volunteers, recruited during a 6 month intake phase from six randomly selected programs in Philadelphia. The service involvements of all clients will be assessed at intake and at 3 months, 6 months, 12 months, and 18 months from their point of intake. Counselors and case records will also be interviewed and reviewed at these points in times for those clients who remain active. For clients who leave treatment, community follow-up will be conducted at their scheduled interview points. Changes in client status (outcome) will be related to their service involvements, demographic characteristics, and program characteristics. From a practical viewpoint, obtaining an understanding of the relationship of service involvement, client and program characteristics on the one hand, and treatment outcome, on the other, will allow for (a) the development of predictive models of treatment outcome relative to treatment process and client characteristics; (b) the identification of the relative power of various treatment elements in terms of their relative contribution to treatment outcome, and (c) the potential development of an empirically basis for the assignment of clients to treatment(s) based upon the predicted response of specific "types" of clients to specific "types" of programs. Based upon these analyses, a typology of service involvement patterns will be developed and used to provide an understanding of the relationship between treatment process and outcome contributing to an increased understanding of the power of treatment in the process of rehabilitation.